The invention relates to an inserter for vacuum installations, having a bipartite arm provided with a driving end, a single joint and an end for holding an object. The arm can turn in at least one horizontal plane about a vertical main axis disposed in the area of the driving end, and has at least one motor for moving the arm about the main axis and changing the angle between the parts of the arm at the joint.
In printed literature of Brooks Automation of North Billerica, Mass., U.S.A., an inserter of the kind described above is disclosed, in which two bipartite arms are disposed with a main axis on a rotatable platform in a mirror-image arrangement, and are articulated at their outer ends to a carrier plate for the transport of wafers. The driving ends of the two arms are mounted each over a shaft in the platform, while the two shafts are spaced apart from one another. Roughly speaking, the two jointed arms form a parallelogram, which can also be seen as a section of a scissors drive. By the appropriate control and superimposition of radial and tangential movements, a circular area can be swept by this known system, although the entire mass has to be accelerated and retarded each time the system performs a turning movement. Also, the system has a great number of pivots and joints which are disposed within the vacuum and therefore are difficult to lubricate. For this reason, and on account of the many joints and bearings, wear inevitably occurs, which is an extremely undesirable factor in numerous production processes.
The published German patent application No. 24 02 026 has disclosed a linear crank drive in which the two equally long parts of a bipartite lever are driven with a transmission ratio of 2:1 by a common drive, so that a point "P" of the application of power to the free end of the lever will perform an always rectilinear movement. By rotating the entire system it is possible to address all points within a circular area. Owing to the positive coupling of the two parts of the single lever, however, it is not possible in case of necessity to perform movements independent of one another of the two parts of the lever. If such a linear drive is disposed in a vacuum, as it is intended to be, the majority of all the joints, including the drive parts for the positive correlation of the movements are disposed in the vacuum. Sliding movements are avoided, but rolling movements take place, so that such a system cannot be used in vacuum installations which serve, for example, for the production of integrated semiconductor circuits.
In the manufacture of integrated semiconductor circuits, wafers are subjected to a multi-step process (metallizing, etching, oxidation) in a vacuum. The wafers pass successively through several processing chambers in which the actual processing is performed. An important problem involved in this production process is created by dust particles which settle on the wafer and then result in faults in the circuits. The entry of dust particles from the outside and their production inside of the apparatus must therefore be prevented insofar as possible. Dust is formed inside of the apparatus by surface wear between moving parts, since reliable lubrication in the vacuum is virtually impossible. A decisive factor in the success of such an apparatus, therefore, is a wafer transport mechanism which involves the lowest possible number of components subject to wear. This requirement is further complicated by the working temperatures commonly involved, of about 250.degree. to 300.degree. C.
Furthermore, it is desirable that the transport movement of the wafers be as free as possible of vibration, since the wafers are very brittle, especially in sizes of 200 mm and more. Also the reliability and therefore the simplicity of the transport mechanism must satisfy stringent requirements allowing no more than one error to about 10,000 movements. Since the wafer processing systems must be set up in extremely clean rooms, they must occupy a minimum of space, since the cost of construction and maintenance per unit area is very high. The chief requirements of a multi-chamber system for the processing of wafers relate not only to the working process itself, but also safety of operation, freedom from foreign particles and compactness of the parts of the mechanical transport system.
The present invention therefore addresses the problem of devising an inserter of the kind described above, whereby delicate objects can be transported in a simple, safe and contamination-free manner between the various stations of a vacuum system.
Stations, in this sense, are the process chambers themselves, in which processes such as plasma etching, oxidizing and metallizing, for example, are performed, as well as the loading and unloading stations of the system. The last are usually in the form of cassette insertion and removal stations.